A bit of forgetting about being a patron and sunken cost ("I've spent hundreds of dollars and waited years, if I stop supporting now the devs might never finish the game").The funny part is that even when a game hits that late stage of abandonment about 1/4 of their patreons still pay out, dunno if it's wishful thinking of poor management of outgoing expenditures.
And new games serve the purpose of getting new supporters. After waifu academy, harem hotel and this, I've learned the lesson that a game is on the path of no return the first time a following update takes more than a couple of months